Nov. 13 — Here’s a sobering thought: While you’re looking at your computer, it may be looking back at you. There is easy-to-get, even free, software that lets anybody spy on you, anytime you are on your computer.

Last week, KNTV and MSNBC.com examined online infidelity and found Internet temptation is quietly on the rise. It turns out, so is the prevalence of spy software designed to catch a cheating lover.

Virtually anyone with an e-mail inbox knows about the software, which is being aggressively hawked by spammers. Programs with names like “Email P.I.,” selling for as little as $50, promise to let a buyer peek over the shoulder of anyone, anywhere on the Internet, while he or she sits at the computer. Another such program, named “Internet Spy 2003,” says in its e-mail pitch “Investigate anybody-anytime!!”

“Utilize these powerful Internet resources to locate people, run business investigations, find legal information, contact long lost friends or just snoop around,” says a Web site advertising the software. “Internet Spy is an amazing tool that will help you find just about anything about anyone. You can use it in the privacy of your own home without anyone ever knowing, ... Don’t hire a private investigator. Do it yourself with Internet Spy.”

Most spyware is simple. It digitally stores copies of everything that’s typed on a computer. Then, the information can be secretly e-mailed to the amateur spy at regular intervals.

Monitoring software of all kinds continues to flood the Internet. Earlier this year, the Aberdeen Group said some 7,000 such programs were in circulation around the globe. But the term “spyware” is a bit controversial. Monitoring software runs the full spectrum from clearly illegal to relatively innocent marketing tools. At the sleazier end of the spectrum are silent hacker programs designed to work like wiretaps, stealing every credit card number and password a victim types. On the other end are so-called adware programs, which anonymously watch an Internet browser’s activity and display context-sensitive advertising. Adware companies bristle when they are lumped together with spyware designed to snoop on cheating spouses.

It’s easy to understand why: Spyware software is alarmingly invasive. It can be slipped onto an unsuspecting victim’s computer disguised as a simple e-mail, or even a greeting card. Once installed, it is virtually undetectable by the naked eye. Even virus protection software — or the best-laid security plans — usually won’t spot it. It doesn’t ask you to download any attachments or answer any questions, it just automatically installs itself on your system

But once it’s on your system, it can tip someone off to everywhere you visit on the internet, every e-mail you write, every password you enter.

“It’s so easy, people have started using spyware to track their children, employees, ... even their spouses,” said Keith Krasnove, a private investigator for more than 30-years. Spyware, he said, is the most sophisticated way ever to check up on your partner.

“Usually what happens is a spouse detects a change of attitude, perhaps less intimacy between them,” he said. So the suspicious partners turn to software to confirm their suspicions.

In a few minutes, users can trace everywhere their spouse has been surfing, and everyone he or she has been communicating with.

“There is no privacy. There is no safeguarding of privacy,” Krasnove said.

One way Internet users may think to protect their privacy is to buy anti-spyware software, another Internet niche which has quickly sprouted up in reaction to the spyware craze. But consumers trying to fight back against the snooping need to exercise plenty of caution and skepticism. Anti-spyware software often isn’t quite what it appears to be, either. Some programs install themselves on a victim’s computer, then display a pop-up box which claims there’s spyware on the machine, and offers to remove it — for a fee.

Free programs such as Spybot Search and Destroy can be used to discover and remove spyware programs.